In the area of reproductive physiology we wish to determine: 1) the neural and endocrine factors which are implicated in the transition of the anestrous ewe to first heat; 2) whether alterations in gonadotropin and prolactin levels occur in male odor-stimulated responses in female mice, and whether the changes are the same in estrus synchronization, pregnancy block, and advancement of puberty; 3) whether the pregnant mouse has a twice daily surge of prolactin, and the significance of those surges; 4) whether extracts can be prepared from testes which are capable of selectively depressing FSH levels, and to identify the responsible factors in such extracts; and 5) whether progonadotropic and antigonadotropic activities present in sera of mares immunized with HCG are resident in the same molecule. Objectives of other studies are: 1) to continue to explore the mode of action of MSH in promoting darkening of hair in agouti mice, trying to determine in tissue culture studies whether effects on color, tyrosinase activity, and pigment granule ultrastructure are interdependent; 2) to evaluate the possibility of an intercellular site of action of polypeptide hormones and catecholamines; and 3) to purify further pharmacologically-active compound(s) of the urophysis and to attempt to develop a system for maintenance of the urophysis in organ culture. BIBLIOGRAPHIC REFERENCES: Geschwind, I. I., R. Dewey, J. P. Hughes, J. W. Evans, and G. H. Stabenfeldt. 1975. Plasma LH levels in the mare during the oestrous cycle. Journal of Reproduction and Fertility, Suppl. 23: 207-212. Pearson, D., and I. I. Geschwind. 1976. Mechanism of action of melanocyte stimulating hormone: Mouse coat color changes in organ culture. Federation Proceedings 35: 687.